This invention relates generally to marine propulsion engines, and more specifically, to determining atmospheric pressure and exhaust back pressure.
Fuel flow to cylinders in engines including electronic fuel injection systems typically is adjusted based on a number of engine operating parameters, including air flow. For example, as air flow to the cylinders increases, fuel flow to the cylinders also must increase in order to maintain good combustion. As air flow to the cylinders decreases, fuel flow also must decrease.
Fuel flow to the cylinders also is adjusted based on operating parameters such as atmospheric pressure and intake air temperature. An absolute pressure sensor typically is utilized for generating a signal representative of atmospheric pressure, and a temperature sensor typically is located at the engine air intake to generate a signal representative of intake air temperature. The sensors are coupled to, or part of, an electronic control unit (ECU), which samples the signals generated by the sensors and adjusts fuel flow according to the sampled signals.
Another parameter that has a significant impact on air flow through the engine is exhaust back pressure. Specifically, outboard motors vent exhaust gases downwardly through an exhaust housing to a through-the-hub propeller. Hydrodynamic effects due, for example, to propeller rotation, impact the exhaust back pressure. Increased back pressure can restrict or prevent the venting of exhaust gases.
To determine exhaust back pressure, a pressure sensor can be added in the exhaust flow path. Adding a pressure sensor, however, increases the engine cost and complexity. Further, by adding another sensor, engine reliability may be adversely impacted since an extra sensor increases the possibility for a sensor failure.
It would be desirable to enable determination of both atmospheric pressure as well as engine exhaust back pressure, yet avoid the extra cost and complexity, and reliability concerns associated with adding an additional sensor to the engine.